The manufacture of conductive papers has received widespread attention over the years. Thus, for example, B. B. Gutman, a Russian, published an article entitled "Electroconductive Paper", in Bumazhnaya Promyshlennost' 31, No. 6: 12-15 (1956), wherein he reported on his investigations into the use of various materials to improve the electroconductivity of paper. His investigations showed that carbon black or graphite, when introduced into paper as a filler, imparted satisfactory electroconductivity to the paper. Gutman's work also revealed that with an increase in the number of electroconductive plies in a sheet of paper, the electrical resistance of the paper is increased while the mechanical retention of the conductive particles is weakened. The papers used in the investigations of Gutman were prepared from unbleached sulfate pulp using a beater.
In U.S. Pat. No. 3,149,023 there is disclosed a graphite containing fibrous sheet material having electrically conductive properties. The sheet material is prepared by a multi-step process which includes admixing graphite particles with fibers of papermaking length in water to provide a homogeneous slurry. The slurry is then fed to the headbox of a paper making machine into which is fed simultaneously therewith a solution of a cationic agent, in particular, an amine-modified starch, so that the two feeds intermix but a very short time before the fibers and graphite particles deposit upon the wire of the papermaking machine to form the initial electrically conductive sheet material. The graphite particles employed in the process of the patent are less than 200 mesh and preferably less than 300 mesh, and the end product comprises 30-75 percent graphite particles by weight. According to the teaching of the patent, the cationic agent used is believed to develop a strong positive charge on the graphite particles in the aqueous slurry with the fibers, and that the graphite particles then flock and are attracted to the surface of the fibers which acts as if negatively charged. Following preparation of the initial or base conductive sheet material the sheet material is dried, and then impregnated or saturated in a dispersion of graphite particles in a resin such as chlorinated natural rubber. The excess dispersion medium is removed, and the thusly impregnated sheet material is dried. The dried sheet material thereafter is subjected to a supercalendering operation wherein the sheet is compacted and the graphite particles crushed to form the finished sheet material.
In U.S. Pat. No. 3,265,557 there is disclosed a process for making electrically conductive products comprising a mixture of electrically conductive carbon fibers and natural or synthetic non-conductive fibers. The process is carried out by dispersing the carbon fibers in a liquid slurry, and agitating the slurry to disperse the carbon fibers in the form of individual filaments. The non-conductive fibers are then added to the slurry, and the resulting mixture is felted. The semi-dried sheets are dried in a press under pressure. According to the patent, a plurality of the separately formed sheets can be fused together at elevated temperatures to form a single sheet.
Other patents directed to electrically conductive products, and processes for manufacturing them, include U.S. Pat. Nos. 4,160,503, 4,211,324 and 4,290,070. Each of the patents is directed to containers for dissipating electrostatic charges which may damage the micro circuitry of printed circuit boards. The containers disclosed in the patents are formed from finished paperboard, a surface of which is coated with conductive carbon black particles contained in a printing ink vehicle. In order to provide an effective coating of conductive carbon black on the surface of the paperboard, it is necessary, in practice, to apply at least two coatings of the carbon black-printing ink dispersion on a single surface of the paperboard which, of course, increases production time, and adds to the overall cost of the end product.